The subject of the invention is a device for fastening a variable pitch blade.
Many propeller blades have a variable pitch to optimise their operation. The blade is then extended by a pivot rotating in a housing in the propeller hub, or more generally in a support part. The blade and the pivot are often separate parts, the blade being composed of a composite material to save weight, the pivot remaining metallic to resist the forces applied to it. In a number of designs, the pivot is then built into the blade which is moulded over it, and the two parts are therefore inseparable. This is satisfactory in some aspects, but it has the disadvantages that manufacturing is more complicated and that the blade is thicker because it needs to surround the pivot; and continuity between the bottom of the blade and the support part in which the pivot is housed is not good, which creates aerodynamic losses. Other designs consist of constructing the blade and the pivot separately, and holding them together by a dovetail.
One known design of this type is shown in FIGS. 1 and 2 (or in U.S. Pat. No. 5,263,898). A propeller hub 1 comprises a circular housing in which a pivot 2 is housed, to rotate a blade 3. A groove 4 with a dovetail section and a root 5 of the blade 3 with a corresponding section are shown. Turning is possible due to the roller bearings 6 and the thrust bearings 7 between the hub 1 and the pivot 2. The root 5 of the blade 3 is held in place in the groove 4 firstly by a shim 8 inserted in the groove 4 and secondly by a shim 11 held in place by bolts 12 extending in the pivot 2 parallel to the groove 4 and on each side of it. The bolts 12 are also used to hold the shim 11 in contact with spring 61 positioned in the groove 4 under the root 5 and the function of which is to hold the blade 3 radially in place when the centrifugal force is not sufficient to keep the root 3 in contact with the groove 4, particularly when stopped. The spring 61 is slightly curved at rest and the bearing of the shim 11 applies a deformation curvature on it which holds the blade 3 in position. A toothed ring 60 is held in place around the pivot 2 mainly by a locking sector 13 that closes the ring to which it is screwed, and which is also held in place by bolts 12, supporting the shim 11 from behind. In this design, the pivot 2 may be easily provided with an upper circular platform 14, that projects in the radial direction beyond the main portions of the pivot and the function of which is to restore continuity of the boundary of the air stream.
However, this design has the disadvantage that it requires a large number of parts to hold the blade in the groove. One purpose of the invention is to propose an improvement and thus to facilitate attachment, disassembly or replacement of the blade, and saving weight.